The present invention relates to a technology, used in an image capturing device, for enhancing its activating functionality so as not to fail to capture a desired image of a subject or the like and preventing unnecessary power consumption in a standby state of the image capturing device before it enters an image capturing mode.
A camera-device configuration (see, for example, Japanese Unexamined Patent Application Publication No. 2003-274640) is known which shortens an activation time that is necessary from the time a power-on operation is performed on a camera device until the camera device is actually switched on for use.
When a power supply switch is operated, chattering in which intermittent opening and closing of a contact is repeatedly performed occurs, thus causing a false operation, etc. Accordingly, after a time passes until effects of the chattering disappear, a process (so-called “chattering preventing process”) that determines whether the power supply switch is opened or closed is performed. In addition, when it is determined that the power-on operation has been performed, a system initializing process is performed after power supplied by a system's power supply unit becomes stable. After that, the camera device is in a state capable of processing such as image capturing. In other words, it is difficult to perform an operation or processing desired by a user unless a time represented by “T1+T2+T3” passes after a power-supply operation time at which a power-supply operation is performed, where T1 represents a time necessary for the chattering preventing process, T2 represents a time necessary until the power supplied by the power supply unit becomes stable, and T3 represents a time necessary for the system initializing process.
Therefore, by performing the chattering preventing process after turning on the power supply switch and the system initializing process in parallel, an activation time from the power-supply operation time until the operation or processing desired by the user is initiated can be shortened. In other words, by employing a sequence that performs system initialization as background processing for the chattering preventing process, after the power is supplied to the system, the system can be initialized without waiting for the chattering preventing process to finish. For example, when T1<T3, the activation time can be shortened to a time represented by “T2+T3” or approximately a time obtained by adding some value to “T2 +T3.”
However, the image capturing device of the related art has the following problems in its activating functionality and power saving function.
For example, cases in which the user misses a shutter release opportunity include a situation in which, when the power of the device is off at the time the user finds a desired subject, the user fails to capture an image of a subject due to a long time taken after the user holds the device until the device is ready for image capturing. In other words, a time necessary for activation after pressing the power supply switch is no more than approximately one second, even if the activation is fast, so that it is difficult to capture an image of a subject (or the like) passing in a moment. This is because it is difficult to reduce the activation time to zero in an actual device. To prevent the user from missing the shutter release opportunity, the system power needs to be continuously on or the device needs to be in a suspend state. The suspend state means a state in which, although an operation of a control unit such as a CPU (central processing unit) is stopped, the power of each portion of the system is on.
As described above, to reduce the activation time close to zero, an increase in power consumption is extremely important and necessary in compensation for the reduction. Therefore, when a battery-driven portable device is used, it is necessary for a user to carry many charged batteries or to use a mass storage battery. In a digital camera or the like, a device power-saving function is important for capturing as many images as possible. Thus, shortening of the activation time and the need of power saving conflict with each other.
Accordingly, it is desirable to satisfy both an improvement in activating functionality and power saving in an image capturing device.